1. Field of the Invention
The present invention is related to a nozzle for an injection molding apparatus.
2. Related Art
Injection molding systems generally include an injection molding unit, an injection manifold and one or more hot runner nozzles for receiving melt from the manifold and transferring/distributing the melt to one or more mold cavities. Hot runner systems offer the choice between thermal gating and valve gating. Valve gating is used in applications where the esthetic appearance of finished molded part is important, because it provides a better gate vestige on the part than thermal gating. One problem with valve pin gating is premature wear of the pin and the nozzle as a result of misalignment of the valve pin; this in turn may cause leakage and poor cosmetic part quality.
Certain known valve-gated hot runner nozzles are not suitable for molding parts that require improved strength or higher esthetic merits. This is because the valve pin behaves as an obstruction in the flow of the melt through the nozzle and towards the mold cavity. The valve pin splits the melt flow and this creates undesirable flow lines that are visible or weakens the finished molded part. In order to utilize a runner system to make injection molded parts of various colors, a first color molten material must be flushed from the system so that a second color molten material may be run through the injection molding machine to produce parts of different color. Residue material from the first/subsequent color of the molten material conventionally causes numerous shots of injection molded products to be defective because they have an undesirable blend of two colors of molten material. It is common for a substantial number of products to be defective in this way requiring multiple injection cycles to clear the runner system before useable products are formed.
Additionally or aside from when color change may be a problem, unidirectional molecular orientation and weld/flow lines can be a potential cause for weakness in the structural integrity, dimensional accuracy, or cause unwanted birefringence of molded products.
Therefore, what is needed is a system and method that substantially reduces residue of molten material in an injection molding machine, while also providing a method that improves valve pin alignment in the nozzle and gate area. Additionally or alternatively what is needed is a system and method for eliminating or substantially reducing unidirectional molecular orientation and/or weld/flow lines in a molded product caused by the valve gating device, such as a valve pin.